Many types of wood preservative treatments exist on the market today. These can be applied directly to the surface, paint-on, or by vacuum pressure immersion treatments. During industrial application of preservatives, timber is typically impregnated with the treatment solution to achieve either shell or full cell type penetration into the substrate.
Depending on the wood species being treated and the end use, the depth of penetration of the preservative solution into the timber can have a significant bearing on the useful service life of the treated timber.
A typical industrial treatment plant will consist of a storage tank to hold the treatment solution and an autoclave. Timber is charged into the autoclave and this is then flooded with treatment solution. Combinations of vacuum and pressure are applied to achieve the required penetration of preservative into the timber.
During the treatment process, an amount of preservative solution is consumed by way of being absorbed into the timber. This typically represents a relatively small amount of the total volume of solution used to flood the autoclave. This generates a scenario whereby treatment solution is repeatedly exposed to timber. The average treatment solution age increases as a function of solution refresh rates. This can extend from several days to many months. Therefore the solution is repeatedly exposed to timber.